Bertelmann, Thomas
Strodthoff, Stefan
Sekundo, Walter
Mennel, Stefan
Article History
Received: 19 April 2017
Accepted: 21 June 2017
First Online: 3 August 2017
Conflict of interest
: T. Bertelmann, S. Strodthoff, W. Sekundo and S. Mennel declare that they have no competing interests.